Heaping and secondary flows in sheared granular materials

Ralf Stannarius,David Fischer,Tamás Börzsönyi

doi:10.1051/epjconf/201714003025

Abstract

Split-bottom cylindrical containers are well established devices in experiments where granular materials are continuously sheared. They are characterized by localized broad shear bands. In such shear experiments, shape-anisotropic grains develop a secondary flow profile in the radial direction. A macroscopically observable consequence is the formation of a heap in the center of the container. This effect is found for all investigated types of prolate and oblate grains, but it is completely absent for spherical particles. There are qualitative differences in the behavior of short (moderate aspect ratio < 8) and long grains. The fill height of the granulate in the container considerably affects the time scale for heap formation, while the height of the heap is less dramatically influenced. Under reversal of the shear direction, the heap collapses within a few rotations, before the secondary flow in the reverse direction establishes a new heap.

Highlights

Granular flows are present in countless processes encountered in geology, transport of materials like sand, coal or ores, and agricultural products
We discuss experiments in the geometry of Figure 1a: The formation of the heap extracted from the optical analysis of the surface profile is shown in Figure 3 for particles of different aspect ratios
Heaping is observed for all investigated anisometric grain types, there is no clear trend in the final heap height vs. particle aspect ratio

Summary

Introduction

Granular flows are present in countless processes encountered in geology, transport of materials like sand, coal or ores, and agricultural products. It affects our everyday life in the kitchen or offices whenever we stir or shake grainy matter or pour it out of a container. While flow in Newtonian fluids has been well understood for centuries, and even many non-Newtonian flow phenomena are well characterized in liquids, granular flows have still preserved their mysteries to a great deal. Different aspects of granular dynamics were discussed in books and review articles Peculiarities of shape-anisotropic granular matter have been reviewed recently [6], with focus on specific packing problems, shear flow, alignment and orientational order

Experimental method

Results

Discussion and Summary